In order to open or close the cylindrical pouring spout formed to a packaging container, there is provided a mouth plug structure in which an open/close cap is screw-engaged with a mouth portion of the pouring spout to be detachably. With such mouth plug structure, in order to surely hold the open/close cap to the pouring spout, there is known a structure in which a band is provided around the cap body so as to hold the outer surface of the pouring spout by the band (for example, refer to the following Patent Publication 1).
The open/close cap of such structure is constructed such that the band is disposed on the outer side of the cap body and the band is connected to the cap body by means of coupling piece. Further, the band is composed of a plurality of circular-arc-shaped band pieces which are connected to each other through a connection piece. Engaging pieces projecting toward inside are formed to the end portions in the circumferential direction of the inner surfaces of the respective band pieces, and these engaging pieces are engaged with the peripheral surface of the pouring spout of the open/close cap to thereby hold the cap to the pouring spout.
On the other hand, to the outer peripheral portion of the pouring spout, there is formed a claw portion projecting radially outward. When the cap is opened, the claw portion applies a load to the coupling pieces and the connection pieces to cut them off. That is, when the cap is rotated, the engaging pieces formed to the inner surfaces of the band pieces are engaged with the claw portions, and when the engaging piece is engaged with the claw portion, the load is applied to the coupling piece and the connection piece, thus cutting them off. According to such operation, engaging force of the engaging pieces to the pouring spout is loosened and the cap is therefore freely rotated around the outer periphery of the pouring spout.
The cap of such character is not opened when the coupling pieces and connection pieces are not cut off and the band pieces are mutually connected, and when the cut condition is observed, it is found that the cap has been once opened. This function will serve as tampering prevention function for preventing the inner content from tampering with mischief to the packaging container.
Furthermore, an open/close cap disclosed in the Patent Publication 2 is constructed such that a band is disposed below a cap body so that the band is connected to the cap body through a coupling piece. The band of this open/close cap is formed with two cut-off portions in its circumferential direction so as to be dividable into two pieces or parts in the circumferential direction. The rear portions of the respective band pieces in the cap opening direction are connected to the cap body through the coupling pieces.
With this open/close cap, a projection provided for the inner surface of each band piece is engaged with a ratchet formed to the outer peripheral surface of the mouth portion of a container to thereby prevent the open/close cap from being rotated in the cap opening direction. On the other hand, when the open/close cap is rotated in the cap opening direction, the projection rides over the ratchet. In this instance, a load is applied to the band, and the cut-out portions connecting the band pieces are cut off.
As mentioned above, by confirming whether the band is cut off or not, the invention disclosed in the Patent Publication 2 can judge whether the cap is opened or not.
Patent Publication 1: Japanese Patent Laid-open Application Publication No. HEI 5-124669
Patent Publication 2: Japanese Patent Laid-open Application Publication No. 2004-51195
However, after the pouring spout of the container has been tightly sealed by the open/close cap, when an external force is applied to the container during a conveyance in a conveyance line or circulation path, there is a fear of the coupling piece and connection piece being cut off. Especially, when the coupling piece has been cut off, the tampering prevention function has not been achieved.
In addition, in the conventional open/close cap represented by the invention of the Patent Publication 2, as shown in FIG. 20, for example, when the caps collide with each other during the conveyance of the containers, there were some cases that the band 100 is pushed inward and then deformed in the radially inward direction. When the caps are left in such deformed state, the cut-out portions 101 connecting the band pieces 100 might be cut off by the radially inward impact, thus damaging the rotation prevention function and opening checking function of the band (band piece) 100. Further, in FIG. 20, reference numeral 102 denotes a projection or protruded portion to be engaged with the ratchet.